Prospects In Various Applications Research Articles

Peculiarities of Surface Breakdown in GaAs Bipolar Junction Structures

An avalanching GaAs bipolar junction transistor can operate as an effective terahertz source or as a superfast voltage/current switch, with each unique function offering prospects for various applications. As the transistor is operating near its breakdown voltage, the most probable destruction mechanism is device shortening at the mesa surface caused by surface breakdown. This manifests itself in measured I -V curves as a “soft” increase in surface current within the voltage range lying well below the volume breakdown. Surprisingly, the mechanism of surface breakdown has not properly been investigated or interpreted, despite the long history of the problem. We show here by comparing experimental results with those of 2-D numerical simulations that the “soft” increase in the surface current is, in fact, a premature breakdown that is suppressed by impact-generated electrons trapped at the surface. These negatively charged surface traps cause expansion of the space charge region and reduce the peak electric field near the surface, thus drastically increasing the voltage range over which avalanching can exist at the surface without fatal current growth. This mechanism explains various peculiar features of surface breakdown and should be taken into account when analyzing device reliability, surface breakdown transients, or passivation methods.

Development for detecting upper atmospheric wind and temperature from satellite

中高层大气风场和温度场是重要的大气基本参数, 其全球高精度测量具有广泛的应用前景, 探测需求日趋强烈. 干涉光谱仪由于其多通道、高通量和高光谱分辨率等优点而成为本项目的首选. 目前被成功应用的干涉式测风/测温仪器主要有Fabry-Perot 干涉仪和广角Michelson 干涉仪两大类. 本文对干涉光谱仪用于中高层大气风场和温度场探测的发展状况进行了分析, 同时比较了几种干涉仪测风和测温的可行性及优缺点, 为中国开展中高层大气风场和温度场星载探测打下基础.

Molecular alignment by trains of short laser pulses.

We show that a dramatic field-free molecular alignment can be achieved after exciting molecules with proper trains of strong ultrashort laser pulses. Optimal two- and three-pulse excitation schemes are defined, providing an efficient and robust molecular alignment. This opens new prospects for various applications requiring macroscopic ensembles of highly aligned molecules.

Advanced coating architectures deposited by pulsed and filtered arc ion-plating

Wear resistant coating systems for cutting tools were designed by using an ion-plating technique on the base of filtered arc evaporation combined with pulsed plasma surface treatment. The deposition of the hard coatings under pulsed ion bombardment of a macroparticle free plasma stream resulted in an improved microstructure of the multilayered coating systems in comparison with conventional arc deposited coatings. The coating architecture of these multilayered systems, designed according to the principle of stacked functional layers, was optimized under the aspect of increasing the life-time of the coated cutting tools. Both laboratory and industrial tests were performed with HSS- and carbide cutting tools for several applications. The characteristic features of microstructure investigated by electron microscopy methods will be discussed. Further prospects for various applications of the mentioned coating technology and corresponding coating architectures are also presented in this paper.

Laser-induced micromass spectrometry of bioorganic molecules and biological specimens

The application of lasers in mass-spectrometric investigations is reported. Attention is focused on the description of a commercial laser microprobe mass analyzer (LAMMA) made by Leybold-Heraeus and on some features of the application of the technique to the study of biological specimens. Methods of preparing biological specimens for analysis are described and approaches to the quantitative and qualitative explanation of the spectra are presented. Characteristic features of LAMMA spectra of biological and biomedical specimens are described. Future prospects for various applications of the LAMMA technique are assessed.

Compact high-voltage accelerators of charged particles in space experiments

Some general problems of design and application of compact devices for the generation of pulse electric fields at a megavolt range in space experiments are discussed. The prospect of various applications of powerful electron beams for active diagnostics of upper layers of atmosphere, radiation belts and the earth's magnetic field is also reviewed. The proposed development of powerful impulsive devices is dictated by limitations of energy resources in spacecraft together with a need to get a good signal-to-noise ratio for reliable data recording. Compact devices which directly transform electric energy of a low-voltage source (solar batteries, chemical elements, nuclear reactor, etc.), into the energy of a megavolt charge particle beam of high impulsive power appear as reliable means for satisfying these requirements. In this paper, the basic practical schemes of energy transformation procedures are considered and the optimal operation parameters of high-voltage storage and transformer systems are discussed. Proper application of combined high-voltage insulation techniques result in the development of experimental models of heavy-current electron beam accelerators capable of generating beams of 300–500 kV, 3–5 kA, with a pulse duration of 15 × 10 −9 sec at a frequency of 10 Hz. Typical applications of electron beam accelerators including the generator of electron-beam-controlled discharge laser beams are also described.